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  • Cambridge University Press (CUP)  (2)
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  • Cambridge University Press (CUP)  (2)
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  • 1
    Online Resource
    Online Resource
    Cambridge University Press (CUP) ; 1982
    In:  Quaternary Research Vol. 18, No. 1 ( 1982-07), p. 91-107
    In: Quaternary Research, Cambridge University Press (CUP), Vol. 18, No. 1 ( 1982-07), p. 91-107
    Abstract: Many cores from the deep basins of the Bering Sea have a thin oxidized zone within otherwise reduced sediment. This oxidized zone began to form about 6000 yr ago and represents an interval of about 3200 yr. Mineralogically, the oxidized and reduced sediments are similar, but chemically they differ. Concentrations of Fe and C are lower, and concentrations of Mn, Ba, Co, Mo, and Ni are higher in the oxidized than in the reduced sediment. Mn is enriched about 10-fold in the oxidized zone relative to its concentration in the reduced sediment, Mo about threefold, and Ba, Co, and Ni about twofold. These data suggest that the oxidized zone developed diagenetically as the result of the balance between the flux of organic matter and the available dissolved oxygen in bottom and interstitial waters. We propose that the Bering Sea was substantially ice covered when global glacial conditions prevailed. during the transition to global interglacial conditions, seasonal meltwater from thawing sea ice formed a lens of fresh water that decreased organic productivity. During the winter seasons, however, sea ice reformed and caused downwelling of dense, oxygen-rich waters to recharge bottom waters. The combination of lower organic productivity and more oxygen-rich bottom water allowed oxidized sediment to accumulate. Once full interglacial conditions were established, the volume of sea ice produced was insufficient to affect either productivity or the supply of dissolved oxygen and so bottom conditions again became reducing. Similar events probably occurred during the onset of global glacial conditions, and similar oxidized layers probably formed at these times. Such oxidized zones are highly unstable, however, in a reducing environment and, once buried beyond the influence of bacterial and infaunal activities, are depleted of their available oxygen and converted to reduced sediment.
    Type of Medium: Online Resource
    ISSN: 0033-5894 , 1096-0287
    RVK:
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 1982
    detail.hit.zdb_id: 1471589-2
    detail.hit.zdb_id: 205711-6
    SSG: 13
    SSG: 14
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  • 2
    Online Resource
    Online Resource
    Cambridge University Press (CUP) ; 1995
    In:  Short Courses in Paleontology Vol. 8 ( 1995), p. 107-118
    In: Short Courses in Paleontology, Cambridge University Press (CUP), Vol. 8 ( 1995), p. 107-118
    Abstract: Diatoms, golden brown algae, are present in most aqueous environments. Within the marine environment marine diatoms occupy the photic zone and represent the lowest level of the marine food chain. Diatoms are either planktonic or benthic and possess an external siliceous skeleton or frustule, that is boxlike in structure. The size of diatom frustules ranges from less than 1 μm to more than 1,000 μm, but most frustules range in size from 10 to 100 μm. Diatoms are present in the geological record from at least the Cretaceous (Harwood and Nikolaev, this volume) and have numerous advantages for biostratigraphic correlation and paleoenvironmental reconstruction of marine sedimentary sequences. This chapter summarizes the current state of marine diatom biostratigraphy for the Cenozoic and provides examples of how marine diatoms are used in paleoenvironmental reconstructions. No attempt is made to illustrate the various diatom taxa discussed; the reader is referred to published references such as the syntheses of Fenner (1985) and Barron (1985).
    Type of Medium: Online Resource
    ISSN: 2475-2630 , 2475-2673
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 1995
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